RUI: Precision Nanocrystallization for Enhanced Strength and Ductility in Bulk Metals

金属坚固耐用，使其能够用于各种性能关键行业，如汽车，航空航天，国防，生物医学植入物等。金属的一个限制是它们的高密度，这降低了它们的强度重量比。金属可以通过将其晶粒尺寸减小到纳米级来显着增强，但这也会使它们变脆。如果金属的强度可以在不变脆的情况下增加，那么总体上可以使用更少的材料，并且可以应用新的设计。本项目将使用一种商业上可行的技术，即表面机械研磨处理（SMAT），研究这种权衡的基本原理。SMAT使用滚珠轴承的冲击力使表面变形并增加其强度。底层材料保持延展性，从而实现强度和延展性之间的平衡。这项工作的目标是量化SMAT过程，并了解基本原理，从而实现优化的冲击能量和位置选择。这将允许处理比目前实际的更大的组件，甚至可以通过其他目前可用的纳米结构化方法来处理。可能从这项工作中受益的行业包括航空航天、能源和汽车。 该项目通过使用新的实验和计算方法将工程理论与高级应用联系起来，为本科生提供独特的研究经验。通过与其他研究机构（如美国陆军研究实验室）的合作，将进一步增加深入培训的机会。金属材料的强度-延展性权衡是一个经过深入研究和记录的现象。这种妥协的严重性已经通过纳米晶金属和合金的发展而得到强调。这些材料可以通过简单的晶粒细化提供显著的强度和硬度增加，但这提出了两个重大挑战：（i）拉伸延展性的相应降低，以及（ii）使用通常与成本有效的批量生产不相容的加工技术。该项目旨在通过开发实验和计算工具来解决这两个方面，以量化纳米晶化过程中由冲击介导的严重塑性变形（SPD）的晶粒细化。这将使用一套定制的研究设备来完成，该设备允许使用表面机械研磨处理（SMAT）将冲击能量和频率与微观结构转变直接相关，从而实现强度和延展性的组合。这将与有限元分析相结合，以验证和扩展该技术，从而创建二维冲击模式，以优化强度和延展性的塑性应变梯度。该奖项的目的是获得关于SPD纳米晶化的基础知识，并利用这些知识以具有成本效益和可扩展的方式制造块状纳米结构金属和合金。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

Metals are strong and durable, which enables them to serve in diverse performance-critical industries, such as automotive, aerospace, national defense, biomedical implants, and many more. A limitation to metals is their high density, which lowers their strength-to-weight ratio. Metals can be significantly strengthened by reducing their grain size to the nanoscale, but this can also make them brittle. If the strength of metals can be increased without becoming brittle, then less material can be used overall, and new designs can be applied. This project will examine the fundamentals of this tradeoff using a commercially feasible technique known as surface mechanical attrition treatment (SMAT). SMAT uses the impact of ball bearings to deform a surface and increase its strength. The underlying material remains ductile, thereby achieving a balance between strength and ductility. The goal of this work is to quantify the SMAT process and to understand the fundamentals, thus enabling optimized impact energy and location selection. This will allow larger components to be processed than is currently practical, or even possible, by other currently available nanostructuring methods. Industries that could potentially benefit from the work include aerospace, energy and automotive. This project provides unique research experiences to undergraduate students by connecting engineering theory to advanced applications using new experimental and computational approaches. Opportunities for in-depth training will be further enhanced by leveraging partnerships with other research institutions, such as the US Army Research Laboratory.The strength-ductility tradeoff with metallic materials is a thoroughly studied and documented phenomenon. The seriousness of this compromise has been emphasized by the development of nanocrystalline metals and alloys. These materials can provide remarkable strength and hardness increases through simple grain refinement, but this presents two significant challenges: (i) a commensurate decrease in tensile ductility, and (ii) the use of processing techniques that are often incompatible with cost-effective bulk production. This project aims to address both aspects by developing experimental and computational tools to quantify grain refinement during nanocrystallization by impact-mediated severe plastic deformation (SPD). This will be accomplished using a suite of custom research equipment that allows the direct correlation of impact energy and frequency with microstructural transformation using surface mechanical attrition treatment (SMAT), which allows a combination of strength and ductility to be achieved. This will be coupled with finite-element analysis to verify and extend the technique to create two-dimensional impact patterns to optimize the plastic strain gradients for strength and ductility. The purpose of this approach is to gain fundamental knowledge about SPD nanocrystallization and to use that knowledge to create bulk nanostructured metals and alloys in a cost-effective and scalable way.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.